True, there are purposes for carbon, but the OP is complaining about a foul smelling tank and in this case adding carbon to absorb the odors is a mask for an underlying problem. A healthy aquarium does not smell foul, and my advice is to find the source of the odor. There are only so many things it could be - water, substrate, decor, filter. I would start with a large water change of 50-60% and see how that goes.

True, there are purposes for carbon, but the OP is complaining about a foul smelling tank and in this case adding carbon to absorb the odors is a mask for an underlying problem. A healthy aquarium does not smell foul, and my advice is to find the source of the odor. There are only so many things it could be - water, substrate, decor, filter. I would start with a large water change of 50-60% and see how that goes.

carbon does more than mask...it removes the impurities that cause odor.but you are right something must be producing these at a faster rate than the carbon can counteract them.

When this happened to me, I did a complete investigation with my nose. Try to find out exactly where the smell is coming from. During the cycling process, the water will tend to smell a little foul due to the ammonia as stated earlier, so water changes should reduce this. The smell could also be from decaying food, dead fish, excess waste in the water, so water changes & gravel vac should take care of this as also stated. One unique scenario I had was when I was smelling around when I noticed an odor coming from my tank, I smelled my 2 whisper hand on back filters and noticed the smell was really strong coming from one. There was simply some decaying food caught on top of the sponge of the filter because sometimes I put my pellets near the filter so the waterfall shoots them down quicker. Some must've fallen on the sponge and I didn't notice. So I gave the filter a cleaning and the smell was gone.

It's good to find the source of the problem, rather than treating the symptoms. I have yet to see any water parameter readings, stock level, feeding schedule...

Do the water change any way! and for that 10% water change...If it were me,I'd start doing 25% instead! Leave the 50%'s for monthly ! Also,remember to rinse your new carbon before ya put it in the canister...had a friend who forgot,gads,black water for a bit!!

Sometimes my tank has a smell but I think it's the water that evaporates and collects on the top and edges of the tank. I like the smell...it smells like nature : ) Probably because of the plants. Sorry, I know this isn't very productive input, just my experience.